Many industrial processes are inherently hazardous. These processes typically use toxic, flammable, or reactive materials, and often at elevated temperatures and pressures. In the event of equipment malfunction or human error in these processes, a catastrophic event may occur. Safety instrumented systems (SIS) are automation systems designed to prevent these events. Interest, particularly in the chemical, petro-chemical, and refining industries, in these safety systems has increased recently due to international standards. In such safety instrumented systems, it is important to be able to diagnose malfunctions of the devices in the system.
In industrial processes where toxic gases are used, it is important that the detectors of such gases be constantly able to detect the presence of such gases. This is so even when the normal operating environment has virtually none of such toxic gases present. Moreover, such sensors and detection systems may be deployed in or around such hazardous industrial processes for a period of many years. When a release of toxic gas occurs, it is important that the sensor function effectively to quickly sense the toxic gas such that remedial action can be taken.
Electrochemical sensors are sometimes used within toxic gas detectors as the sensing element. With such sensors, the presence of a gas of interest causes an electrical change in the sensor that can be detected by suitable sensing circuitry. Examples of electrical characteristics include voltage, resistance, reactance, capacitance, or any other suitable electrical parameter.